Mandy Brown Belfort, MD MPH is a neonatologist at Children's Hospital Boston and Instructor of Pediatrics at Harvard Medical School. This application for a K23 mentored career development award combines structured mentorship and training with a detailed research plan. The overall goal of this proposal is to train Dr. Belfort for a career as an independent patient-oriented researcher focused on the long term outcomes of early-life growth and nutrition. In full term infants, rapid infant gain is associated with long-term risks, such as overweight and high blood pressure, but whether rapid weight gain is similarly harmful in preterm infants is unclear. Rapid weight gain may also be beneficial, for example to neurodevelopment in preterm infants; whether rapid weight gain benefits neurodevelopment in full term populations is poorly understood. A better understanding of the balance of risks and benefits associated with rapid infant weight gain in both full term and preterm populations would inform guidelines for optimal infant weight gain patterns in these populations. For this award, Dr. Belfort aims first to assess the adiposity-related risks and neurocognitive benefits at school age associated with infant weight gain in 2 large, established cohorts of full term and preterm infants. Dr. Belfort will then build a decision analytic model to estimate the optimal rate of weight gain for full term and preterm infants, balancing adiposity-related risks with neurocognitive benefits through adulthood. This research plan builds directly on Dr. Belfort's previous training in epidemiology and health services research and her clinical expertise in neonatology. Her findings will provide critical information regarding patterns of weight gain that optimize long term health in full term and preterm populations. Dr. Belfort's unique resources include a supportive, accomplished multi-disciplinary mentorship team; access to 2 large, established, longitudinal cohorts of full term and preterm children; and advanced coursework in epidemiology and decision analysis. The proposed award will enable Dr. Belfort to make a substantial scientific contribution and to develop her career as an independent investigator.